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A transistor mainly has three terminals, which are connected to the emitter, base and collector respectively. The working system of the transistor operates only because of 3 ends. These transistors are used in most of the electric devices nowadays. They are very cheap and are also small in size.

Transistor first end: emitter (E)

This is the left region of the transistor end, and its main function is to supply the majority of charge carriers. The electrons are the majority charge carriers for the NPN. The holes are the majority charge carriers for PNP.


The emitter (E) is always placed in a forward bias state with respect to base (B) so that it can easily supply the majority of charge carriers in base (B). The doping of the emitter (E) is always done to a large extent so that it can supply only a large amount of charge carriers.

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Other end of the transistor: Collector (Collector, C)

Its main function is to collect the majority charge carriers. The collection is added in the posterior bias state.


Third end of transistor: Base (Base, B)

It is the central part of the transistor and its doping is kept very low and it is kept thinner (of the order of um) than the emitter and collector so that it can send almost all the charge carriers to the collector.

Here it is necessary to know that emitter (E) and collector (C) cannot be interchanged (i.e. C across the place of E or E at the place of C) because physically the size of the collector (C), emitter (E) is higher than that. The main reason for keeping the size of the collector large is that while the working of the transistor, a lot of heat is generated at the collector joint, which is very important to absorb. The symbols of the transistor are shown in the figure below, in which the arrow is always shown at the emitter end and its direction shows the direction of current flow.

In PNP transistor the current flows from E to B and in NPN transistor the current flows from B to E.

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